The present invention relates to a method of preventing or reducing linting and/or smudging on resin based printing plates by treating with a surface treating agent. In the method of the present invention the surface treating agent is an anionic, cationic or ampholytic fluorocarbon having a perfluoroalkyl group with 4 to 14 carbon atoms. The fluorocarbon of the present invention may be used in aqueous, alcohol or aqueous-alcohol solution to pretreat relief printing plates and prevent or alleviate smudging.
In the past, the plates generally used in high-speed rotary presses such as those used in newspaper printing were metal, for example zinc or aluminum. However, in recent years the trend has been away from use of the conventional metal plates and towards use of resin based plates. A variety of resins have been used in forming resin based plates, however, in general the resins chosen are photo-sensitive.
The change to resin based plates was due to lower cost and increased ease of handling. Although the resin based plates are easier to work with, they have the disadvantage of allowing ink to build up in the depressions (concave sections) of the relief printing plates. When ink builds up in the depressions of the image, smudging of the dots occurs. Although the mechanism of this smudging is not fully understood, it is known that when ink or dust accumulates in the depressions of a relief plate during printing smudging occurs and results in a reduction of the halftone grid quality.
In the past, smudging was prevented by treating the resin plates with agents which were made by dissolving silicone oil in a hydrocarbon solvent or with agents which were water repellent and oil repellent. However, it was found that agents which were made by dissolving silicone oil in hydrocarbon solvent were not sufficiently durable because they dissolved easily in the ink. As a result, smudging occurs after about 20,000 impressions. The latter type of agent is not effective unless complete heat-curing is conducted after the pretreatment. Additionally, even if heat-cured, smudging occurs in plates treated with agents of the latter type after about 30,000 impressions.
It is an object of the present invention to provide a method of treating a printing plate with to surface agent which prevents or alleviates the smudging of dots in relief printing plates used in high speed rotary presses, particularly those used in newspaper printing.